Detecting when alternating current (AC) voltage and/or current waveforms cross through a zero current (or voltage) axis (e.g., “zero crossing”) is frequently performed, for example in electric motor control, lamp dimming, powerline communication and other applications. In motor control systems, a half-bridge circuit is frequently used to drive a switching node coupled to a load (e.g., the motor). There is difficulty in robustly detecting the zero-crossing when the switching node is noisy.
Switching node noise is a particular issue when MOSFETs are employed as power switches (e.g., in the half-bridge circuit) for a motor control. Motors tend to present an inductive load to the half-bridge circuit, and the combination of the inductive load with the capacitance of the MOSFETs can cause ringing on the switching node, making accurate detection of the zero crossing difficult.
Therefore, an improved zero crossing detector is envisioned to more reliably and accurately detect zero crossings of a current (or voltage) waveform of interest.